USD in AEC

USD and the AEC industry

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Data interoperability is a persistent challenge in AEC that never seems to get resolved. But BIM 2.0 demands a solution, because continuing to isolate data in deep proprietary canyons is increasingly unworkable for firms. Martyn Day takes a look at Pixar’s USD and the newly formed Alliance for OpenUSD’s work to make it a widely accepted standard


If there’s one thing that has ham strung the digitisation of AEC, it’s data incompatibility. Our authoring tools have created a landscape of silos. These, in turn, create in-house and external challenges for individual practices and the federated networks of firms that put together buildings and infrastructure.

On major projects, data wranglers are common, but our industry data exchange formats still don’t work as well as we would like. Data should flow to and from project participants like water, and preferably not raw sewage.

Currently the industry supports a wide range of standards. To name but a few, there’s IFC, BCF, CityGML, gbXML, OpenCDE, SAF, STEP, glTF and OBJ. So it cannot be said that we haven’t had a good old go at solving the issue. Unfortunately, there is still no format to rule them all, and I am not sure there ever will be. And so the work continues.

BIM 2.0 promises a move away from files to databases. The idea here is that this shift will enable granular streams of design data to flow between users, as opposed to big, lumpy files. These cloudbased systems will be containers and hubs within themselves, and APIs (application programming interfaces) will enable access to and collaboration between different applications. At least, that’s the hope.

However, all this is some way off. For now, the latest open format to come to market is one that was never intended to be used in AEC at all.

Enter USD (Universal Scene Description), a format developed by computer animation film studio Pixar. Its original purpose was to make it easier to exchange complete scenes, geometry, materials, lights and cameras between individual departments, allowing simultaneous development for each discipline and bypassing the silos of proprietary formats. Pixar ended up building a whole workflow around USD, which it continues to use today in order to make movies.

In 2021, Nvidia brought USD into the minds of architects and designers with the launch of Omniverse, a design collaboration and simulation offering. Omniverse is based on USD, but is focused on the AEC and manufacturing sectors just as much as it is on the movie industry.

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One can easily imagine an application that receives BIM graphics via a streamed USD in the background, lightweighting the application and securing original data behind Autodesk’s firewall

The system has been trialled by over 400 companies, including Foster + Partners, BMW, Industrial Light & Magic, WPP and Ericsson. Plug-ins have been added to the core design tools, including Revit, Rhino, 3ds max, SketchUp and many others, and data is streamed to the Omniverse environment, which can handle large datasets, rendered in real time, enabling the collation of model data for whole projects, with all disciplines included.

At the time of Omniverse’s launch, Martha Tsigkari, head of the Applied Research and Development Group at Foster + Partners, explained the impact of using USD-based workflows: “Omniverse is a revolutionary platform that has allowed our designers to collaborate and visualise multiple design changes to a scene simultaneously while working on their software of choice.

“As we can review design options in parallel, we have much more time for creative design and visualisation. Integration of futuristic technologies such as machine learning will bring more opportunities to assist the creative process in the future.” Foster + Partners remains an advocate of Omniverse.

Nvidia also launched a herculean effort to create applications within Omniverse, for compositing models from different sources, rendering and viewing, as well as for simulation — all powered by its Nvidia RTX GPUs. At launch, the industry jumped in too, with Bentley Systems, Adobe, Autodesk, Epic Games, Esri, Graphisoft, Trimble, McNeel & Associates and Blender all supporting this USD capability.


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Wrangling dumb geometry

Since the USD format was developed for Pixar, its core capabilities are somewhat biased towards dumb geometry, materials and rendering, and not the metadata layered inside manufacturing and BIM systems. This is an obvious limitation if you want BIM functionality, but Pixar had no need for this capability when it developed USD.

Nvidia, however, was able to scrape some additional metadata from BIM models and add it to USD. This additional information, however, remained ‘dark data’ to other users with USD viewers, because it was not defined in the Pixar USD format. In other words, this was Nvidia’s ‘special sauce’.

From my conversations with folks at Nvidia, obvious frustration is evident with the limits of USD when it comes to the rich data that BIM tools encompass. There has been talk of slamming USD and IFC together, but two open formats combined do not make a third open format. Plus, there is an inherent danger in software firms unilaterally extending the USD format for their own undocumented use. It’s potentially a ‘death by a thousand variants’ situation.

The expansion of USD to something a bit more ‘BIMmy’ is an approach that other firms in AEC have also advocated, especially Autodesk, where development teams were very excited by USD’s potential in all the markets serviced by the company. But how was this to come about, and would Pixar even be interested?

This year, a response finally came. Shortly before the computer graphics event Siggraph in August, the Alliance for OpenUSD (AOUSD) was established. It’s headed up by Pixar, Adobe, Apple, Autodesk and Nvidia, with the aim of augmenting and standardising an OpenUSD specification. Further out, the goal is to achieve ISO standard status.

While this may come as a surprise, USD as it stands today may be open source, but it’s not a standard – it belongs to Pixar. To move from being open source to being a true standard requires a clear, agreed-on specification and a groundswell of relevant support.

Not-so-rebel alliance

“The Alliance for OpenUSD is an open, non-profit organisation dedicated to fostering standardisation, development, evolution and growth of OpenUSD. Through the Linux Foundation, which hosts OpenUSD, new members are encouraged to join and participate,” explained Steve May, CTO of Pixar and chairperson of AOUSD, at the August 2023 launch.

“So, why do we need an OpenUSD? Well, USD isn’t used by many companies. It is not actually an official standard. In today’s world, we have accepted standards for things like text and photos and video — but not complex 3D content.”

To achieve the full potential of OpenUSD, he continued, it needs to work across many platforms, on many kinds of devices, reliably and for years into the future.

With huge firms backing and now actively shaping USD, its future ubiquity is looking like a good bet

“So, the job of the Alliance has two parts. The first is to take the opensource project that Pixar created and make a specification that will enable it to become an international standard, that can be used by anyone worldwide — just like the standards we use today, such as JPEG or H.264, HTML, or other standards. And the second thing is to continue to evolve and advance USD in ways that best serve the OpenUSD broader community.”

The potential applications for OpenUSD are huge, May explained, which makes its development both exciting and challenging. “USD is applicable to anything related to 3D content, whether it’s more scientific applications, or other things. A lot of these areas also have overlap. So, benefits in one field may be very specific to something like industrial applications for scientific visualisation, or also have an overlap with what we do in entertainment.”

At the start, the Alliance will have its own standards body during incubation, in order to get the specification to a point where it can be moved on to a more common standards body such as ISO. At the time of launch, there were no specific plans expressed for AEC workflows, but both Nvidia and Autodesk are obviously interested in expanding its capabilities in this area.

Autodesk talks USD

Speaking with Autodesk’s VP of software architecture, Oliver Goldman, I asked what Autodesk might add to USD and whether we could expect to see an AECspecific ‘flavour’ of USD.

“That’s what we all want to find out,” he responded. “I think it must be a joint conversation. What’s exciting about setting up the Alliance for OpenUSD is that it’s giving us a forum where we can work with everybody involved as partners and figure out what those answers need to be.”

Regarding the combination of IFC and USD, he added: “You can’t just take two standards and slap them together and expect to get a useful result out of it. I think we have a lot of work in front of us to figure out how we can bring them together in an intelligent way. What I would also point out is that standards in the AEC space are incredibly powerful and incredibly important and they are ever-evolving. There are new standards. There are new versions of IFC. I think to the extent that there’s some convergence in technology and maybe even industries here, we need to look at how to bring these things together. How do we evolve the standards in the AEC world to bring in the goodness of USD and that technology stack?

Early conversations held in advance of the Alliance’s founding focused on the complications and the sheer amount of work ahead. “One of the reasons we want to put this alliance together and have AEC participate is that there’s clearly something to do here. And yet I don’t know exactly what that is going to look like. I do think success looks like something that the AEC industry can see as the next evolution of the standards that we depend on and use today to create built infrastructure.”

His colleague Gordon Bradley, fellow of media & entertainment at Autodesk, agrees. “It’s about making sure that we don’t fragment USD, and we’re looking to do that by promoting interoperability through standardisation. A huge piece of this is going to be working with all stakeholders, including industries like AEC, to understand the things that need to be common to enable the kinds of workflows we want. AOUSD is a really great opportunity, as it’s kind of a missing piece of the puzzle, one that gives us an open place to figure that out together. Because, you know, if USD fragments into all those pieces, it’s not going to deliver the promise. It’s not going to deliver the value we want.”

With the expansion of USD, there is also the issue of how much Pixar wants to expand the format? What additions to the core schema make the most sense? One of USD’s current advantages is that it’s lightweight and performant. BIM data, on the other hand, has eaten all the pies! If the aim is to add BIM data to USD, what are the chances of USD sinking under BIM bloat? Since USD variants (USDZ, USDA) already exist, could there be extensions for AEC models?

“You’re raising several concerns – performance, scale, size and the potential bloat of these files. And then another concern is maybe around how many extensions we have? And will that make it difficult to manage compatibility and whatnot? I think you’re very quickly identifying the challenges that we will be working on with our partners in the Alliance,” Goldman responded.

“With respect to the extensions, if we end up with a case of everyone having their own extensions and we don’t have interoperable data, then we probably haven’t done customers a lot of good. And we certainly haven’t met our goals for what we want to accomplish in our AEC portfolio with Forma [Ed: Forma is Autodesk’s AEC cloud-based platform]. We hope to very much work against that,” he continued.

“I don’t see any reason that we can’t avoid that outcome with respect to the amount of data and how we integrate all of that into USD. I don’t think we know the answers to that yet. There are plenty of techniques for data modelling and data serialisation that can be brought to bear on problems like this. I think what’s great about the Alliance is being able to sit down collectively with partners like Adobe and Nvidia and others and say, ‘Okay, out of these options that we have, let’s find the one that works collectively across the board’, so that we can get that singular approach and get the consistency and make it work.”

According to Bradley, the formation of AOUSD is an acknowledgement that to take USD to the next level, to see it play an active role in industries like AEC and also work on browsers, mobile devices and so on, it simply can’t be owned and managed by any individual company. It can’t reach the scale it needs to become a standard under such conditions.

“That’s really the big step up we’re taking here with AOUSD – moving USD out into an open standard, where we can bring the right stakeholders in around it and make good decisions together, and document those decisions, so that one pull request to the GitHub can’t break the behaviour in a web browser or in an AEC workflow.”

The plan is to have a set of working groups in which stakeholders with specific domain expertise come together. These will operate under the framework of a technical advisory committee, which has the responsibility to look across all of USD and ensure that the principles of the data model are respected so that it will keep working for everybody involved.

Nvidia’s take on USD

Guy Martin, Nvidia’s director of open source & standards, has a long history in open source development. In our conversation, he characterised this move as being nothing short of “the advent of HTML for 3D data.” A big claim, indeed.

“With open-source development, it gets to a certain point when it needs to be standardised, as things fragment, and you can’t have that if you want wider adoption. Businesses need to feel that it’s reliable,” he said. The problem with standards bodies, he added, is that getting anything done can take years, “so the plan is to innovate at scale with flexible governance.”

The start point is to develop a core specification working group to look at the code and work out exactly what is core. Other working groups will focus on additional capabilities. And as to what these capabilities might be?

“Well, it’s anything that is 3D content, up to a full virtual replica, like a digital twin or city model,” he replied. “We can’t forget that extended and augmented reality will be ready to consume this data and merge it with the physical world.”

Much of what’s needed really plays to Nvidia’s strengths – GPU acceleration, cloud distribution, rendering views and interaction. And having already invested so much in developing Omniverse, wider adoption of USD as a general business consumption format for 3D would be extremely good news for Nvidia, hence the seriousness of its commitment.

In passing, Martin acknowledged that the Khronos Group’s glTF standard was also a great 3D delivery format and that it is actively seeking to establish a liaison agreement that will see USD and glTF playing nicely together, as they clearly complement each other in terms of application areas.

Work in progress

AOUSD is obviously a work in progress, but it’s good to hear that those involved have very similar outlooks on how it should move forward. It will be interesting to see how long it takes the Alliance to produce something that can actually be used by the industry. There’s a lot of pentup demand, after all. At the same time, IFC 5 has been specified and is in the works, and it’s looking spicy. Who knows: maybe we will be spoilt for choice?

While anything designed by a committee rarely over-delivers, the founding firms are just a handful of big players, with disparate but overlapping interests, suggesting that progress may be made faster than it could be by a larger, more diverse group.

Let’s not forget that Autodesk has Forma to develop. I think USD is something that company executives may be thinking of using both internally and as an interchange format. At some point, the Revit database might be unhooked from Revit and kept only within Forma’s unified database on Autodesk’s servers. One can easily imagine an application that receives BIM graphics via a streamed USD in the background, lightweighting the application and securing original data behind Autodesk’s firewall.

For now, the most immediate winner will be Nvidia, as it already had the foresight to develop a USD-driven platform. Any advances in USD will immediately benefit Omniverse’s data handling capabilities. That said, anything solid could still be two to three years away. With huge firms backing and now actively shaping USD, its future ubiquity is looking like a good bet.


AOUSD members

Founders: Pixar, Adobe, Apple, Autodesk and Nvidia

General Members: Cesium, Epic Games, Foundry, Hexagon, Ikea, Otoy, SideFX and Unity


What is USD (Universal Scene Description)?

Universal Scene Description

USD (Universal Scene Description) was originally developed and open-sourced by Pixar Animation Studios to help its multidisciplinary teams (modellers, renderers, animators, environment artists, lighting and camera operators and so on) share complete 3D ‘scene descriptions’ between a mixture of different software applications. This allows collaboration around work packages containing many gigabytes of data. It also means that a department could be working on the same data in Autodesk Maya, Houdini, V-Ray and Renderman, with USD storing incremental changes and tracking them.

USD supports creating, editing, rendering, and simulating in a common-coordinate virtual space. It is equally applicable to other fields that use 3D, such as architecture, engineering, design, manufacturing, retail and robotics. While it is a file, USD is a multi-format framework that provides interoperability, collaboration, modelling and data interchange and could easily be applied to use in a cloud database.

It has several features that make it a powerful tool for data modelling and interchange:

The composition engine allows users to modify composed ‘scenes’ in different layers, without disrupting the source. This makes it easier to handle large, complex scenes and collaborate

  • USD’s data model is fully extensible, supporting custom schemas, such as the physics schemas developed by Pixar and Apple for rigid bodies, or Nvidia’s Flow for combustible fluid, fire and smoke simulation. This makes USD suitable for a variety of applications and industries such as AEC and engineering
  • USD is ‘system agnostic’, in that it is not linked to any proprietary system and enables dynamic content creation
  • USD uses the Hydra Rendering Framework, which is like Nvidia’s SLI and AMD’s Crossfire technologies, with the key difference of supporting GPUs from different vendors. Hydra interactive rendering mode feeds in-viewport or external rendering engines such as Pixar’s Storm and Chaos’ V-Ray.

USD’s scalability and extensibility, combined with its collaboration potential, make it potentially a very useful format in architecture and engineering. The geometry of BIM models, topology, infrastructure, environment data, materials and physical properties can all be brought together in portable files that contain a virtual world for simulation, analysis and visualisation.


What is Nvidia Omniverse Cloud?

Nvidia Omniverse Cloud is a cloud platform service that enables AEC disciplines to collaborate in a visually immersive environment. This realtime collaborative space facilitates seamless integration of accurate 3D data from disparate CAD and BIM tools in a collaborative virtual world powered by servers stuffed full of Nvidia RTX GPUs for massive, complex, real-time 3D workflows.

Because Omniverse is based on the USD format, different users in a variety of locations, using different software tools such as Revit, Rhino and SketchUp, can collectively work on a building project simultaneously. Users can modify the models, materials, windows, lights and so on, and they can see each other’s changes in real time.

Because it’s Nvidia and its powerful GPUs are at work here, the model can also be photorealistically rendered while all this is being built, complete with sunlight, clouds and materials.


Nvidia Omniverse Cloud


Omniverse can also serve as a platform for basic mark-up comments or to run through multiple variations of a design. Again, using GPUs, analyses and simulations can be run on anything from an individual building to a whole city, such as studies of light, solar gain, wind or pollution. It’s also an environment for third-party software developers to offer their own applications.

At the heart of Omniverse is the ‘Nucleus’, a central hub for managing all the USD elements across various applications, integrating them with the platform. Plug-ins used in core design apps enable real-time transmission of modifications made in Revit, Rhino and so on to Omniverse.

The Nucleus is implemented either on Nvidia’s own servers or on an onpremise basis. It can be hosted on either a server or even a desktop, should your machine have an Nvidia RTX card.

Nvidia has put a lot of effort into its USD environment and shows no sign of slowing down. The latest R&D from Nvidia, demonstrated at SIGGRAPH in August, showed how AI could be applied to a living room scene in Omniverse, to modify brick and materials choices. See below. It’s amazing stuff.


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